feat(frontend): sprint 4 — dark mode + matrix overhaul + tactic selection + done read-only + UI polish

US-17: fix duplicate "Create engagement" button, icon conventions (Save/RotateCcw/Grid2x2), UsersAdminPage form baseline alignment
US-18: done status fully read-only + Reopen button (done → review_required) for all roles
US-19: invalidate engagement queries on simulation PATCH/transition for auto-status propagation
US-20: MitreMatrixModal rewritten — CSS grid 12-column layout, no horizontal scroll, attack.mitre.org compact look
US-21: tactic header clickable in matrix, tactic chips (MitreTacticTag) in field, single atomic PATCH with technique_ids + tactic_ids
US-22: MitreTechniquesField chips-only area + inline search input + matrix icon button; chips show ID-only (name in title=)
US-23: useTheme hook — 3-state light/dark/system, CSS variables, Tailwind darkMode class, localStorage persistence

92/92 tests passing, typecheck and lint clean.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/components/SimulationList.tsx

@@ -96,11 +96,15 @@ export function SimulationList({ engagementId }: SimulationListProps): JSX.Eleme
                   </Link>
                 </td>
                 <td className="px-xl py-md text-charcoal text-[14px]">
-                  {sim.techniques.length === 0
-                    ? '—'
-                    : sim.techniques.length === 1
-                      ? sim.techniques[0].id
-                      : `${sim.techniques[0].id} +${sim.techniques.length - 1}`}
+                  {(() => {
+                    const items = [
+                      ...(sim.tactics ?? []).map((t) => t.id),
+                      ...sim.techniques.map((t) => t.id),
+                    ];
+                    if (items.length === 0) return '—';
+                    if (items.length === 1) return items[0];
+                    return `${items[0]} +${items.length - 1}`;
+                  })()}
                 </td>
                 <td className="px-xl py-md">
                   <SimulationStatusBadge status={sim.status} />